Motors that are incorporated in the compressors of refrigeration and air conditioning devices are required to be energy saving, low-noise emitting, and guaranteed to operate in a high temperature atmosphere of approximately 150° C. Generally, the residual magnetic flux density in a rare-earth magnet that contains Nd—Fe—B is high, and thus rare-earth magnets are suitable for downsized and high-efficiency motors; however, as the temperature increases, a rare-earth magnet's coercive force is reduced. Therefore, when a plurality of motors that include rare-earth magnets and are operated with the same current are used in a high temperature atmosphere, the individual motors tend to become demagnetized. One method for solving this problem is to add a heavy rare-earth element such as Dy (dysprosium) or Tb (terbium) to rare-earth magnets used in a high temperature atmosphere. With this method, the coercive force is improved and the motors resist demagnetization. However, in recent years, the value of heavy rare-earth elements has increased due to their scarcity, and the risks associated with procurement and price hikes are increasing. Due to such problems, there has been a demand for a high-efficiency, low-noise motor that can be used without becoming demagnetized even when it contains a rare-earth magnet that has a low coercive force.
In the conventional technique for a rotor described in Patent Literature 1 listed below, permanent magnet insertion holes are formed in a rotor core in which the plates of a plurality of electromagnetic steel plates are stacked upon each other and voids (flux barriers) to prevent magnetic flux leakage are provided on both circumferential sides of the permanent magnet insertion holes. Furthermore, projections for fixing the permanent magnet are provided on both circumferential sides of the permanent magnet insertion holes. The magnetic flux leakage is a phenomenon where, for example, a magnetic flux at a circumferential end of the permanent magnet leaks to adjacent permanent magnets via an electromagnetic steel plate between magnetic poles; or the magnetic flux is short-circuited in the magnet itself. Therefore, in this conventional rotor, positioning of the permanent magnet is performed and the magnetic flux leakage is reduced, thereby providing a high-efficiency motor.
Furthermore, this conventional rotor is made by combining an electromagnetic steel plate having the projections described above and an electromagnetic steel plate having no such projections. When compared to an electromagnetic steel plate having no projections, in the electromagnetic steel plate having projections, the distance between the surface and the rear surface of a magnet becomes shorter, and thus the magnetic flux tends to be short-circuited in the magnet itself as much as in the projections provided. With this configuration, the permanent magnets can be positioned when inserted into the permanent magnet insertion holes, and by reducing the area of the electromagnetic steel plate having projections, it is possible to provide a high-efficiency motor in which magnetic flux leakage is reduced.